230 J. C. BRANNER OUTLINES OF THE GEOLOGY OF BRAZIL 



the State of Amazonas; they are not certainly known west of 58 degrees 

 longitude on the south side of the valley or west of 60 degrees on the 

 north side. Farther west the Paleozoic beds are concealed by the soft 

 Tertiary and Quaternary deposits that cover thousands of square miles 

 and extend westward to and beyond the Peruvian frontier. Here and 

 there the Archean and Paleozoic beds are cut by dikes of eruptive rocks, 

 but nowhere in the Amazonas region are the dikes known to pass through 

 Cretaceous or Tertiary beds. 



Of the area about tlie headwaters of the Eio Branco but little is known 

 beyond what is to be had from the reports of Brown and Sawkins on the 

 adjoining parts of British Guiana. The areas colored as questionable 

 Cretaceous are merely areas of sandstone resting on the Archean. The 

 rocks have as yet furnished no fossils. 



Of the area between Eio Negro and the Amazon but little is known, 

 further than that it is a flat, forest-covered region of sluggish streams. 

 The country of the western end of the state is represented as Pliocene 

 chiefly on account of the determinations of fossils by Ethridge. (See 

 bibliography below.) The rocks are mostly incoherent sands and clays. 

 The Miocene area, however, embraces large tracts that should properly 

 be shown as alluvial deposits along the streams. Our knowledge of the 

 limits of such areas is too fragmentary to allow them to be sho^m on the 

 map. 



Economic geology. — Gold is said to be found about the headwaters of 

 some of the rivers of the State of Amazonas, but there is no systematic 

 mining of any kind. Limestone is abundant in the Carboniferous rocks 

 exposed along the rios Paranary and Amana and probably also on the 

 Abacaxis. Similar deposits on the Jamunda and Uatuma probably con- 

 tain limestones. Good clays for the manufacture of bricks, tiles, and the 

 common ceramic ware used in the region are abundant, and the Archean 

 region along the upper Eio Negro and Eio Branco furnishes unlimited 

 supplies of excellent granite for building stones. 



Lignite has long been known in the western part of the State of Ama- 

 zonas. It occurs in the fresh-water Tertiary beds about Tabatinga on the 

 upper Solimoes, Javary, and Iga, and it probably has a wide, but uneven, 

 distribution over an enormous area along the Peruvian frontier. Analyses 

 show it to contain about 33 per cent of fixed carbon, about 39 per cent 

 of A^olatile hydrocarbon, and 15 per cent of ash. 



Geologic Maps of Amazonas 



C. Barrington Brown, 1879. — The paper by C. Barrington Brown, "on 

 the ancient river deposits of the Amazon," published in the Quarterly 



